Dope Sheet copy/paste buffer keyframes problem
I think it's a problem of name, don't use "left" or "right", you need to recall all the XXX Left with XXX L or XXX_L or XXX.L, and also make sure all your bones are selected in the 3D view before you ctrl C > ctrl shift V.

About the left fingers: If Blender can't find any bone with R, it can't mirror the right to the left, so give the suffix R to the right fingers.